McArdle Patients Research Articles

Last Word on Point:Counterpoint: Lactic acid is/is not the only physicochemical contributor to the acidosis of exercise

to the editor: We grounded our positions on arguments and quantitative considerations ([2][1]) while the counterpoint supporters often present only statements. Beginning with Van Slyke, we studied a bulk of acid base literature, therefore it is somewhat amusing that we, according to Lindinger and

McArdle disease: Another systemic low-inflammation disorder?

McArdle disease is caused by inherited deficit of human muscle glycogen phosphorylase with subsequent blockade in muscle glycogenolysis. Patients usually experience severe exercise intolerance and ‘chronic’ skeletal muscle damage. We determined circulating levels of 27 cytokines in a group of 31 adult McArdle patients (15 male 16 female; mean (±S.E.M.) age: 39 ± 3 years) and 29 healthy sedentary controls (14 male, 15 female) before and after an acute exercise bout involving no muscle damage (cycling). Patients had an ongoing state of muscle breakdown even when following a sedentary lifestyle (serum creatine kinase activity at baseline of 2590 ± 461 U l −1 vs. 97 ± 5 U l −1 in controls). Under resting conditions, neutrophil count (+20%) and circulating levels of several cytokines were significantly higher ( P ≤ 0.05) in patients than in controls: tumor necrosis factor (TNF-α), interleukin (IL)-1ra, IL-10, IL-12 and IL-17. The myokine IL-6 significantly increased with exercise ( P < 0.05) in both groups. Our results suggest that McArdle disease is associated with low-level systemic inflammation whereas appropriate exercise induces a similar response in McArdle patients and healthy controls, with a significant increase in the anti-inflammatory myokine IL-6. Our results support the rationale for prescribing carefully supervised exercise training in these patients.

AMPD1 Genotypes and Exercise Capacity in McArdle Patients

The purpose of this study was to assess if there exists an association between C34T muscle adenosine monophosphate deaminase ( AMPD1) genotypes (i.e., normal homyzygotes [CC] vs. heterozygotes [ CT]) and directly measured indices of exercise capacity (peak oxygen uptake [VO(2peak)], ventilatory threshold [VT], gross mechanical efficiency [GE], etc.) in 44 Caucasian McArdle patients (23 males, 21 females). All patients performed a graded cycle ergometer test until exhaustion (for VO(2peak) and VT determination) and a 12-min constant-load test at the power output eliciting the VT (for GE determination). We found no significant difference in indices of exercise capacity between CC (n = 18) and CT genotypes (n = 5) in the group of male patients (p > 0.05). In contrast, the VO(2) at the VT was significantly lower (p < 0.05) in CT (n = 4; 7.9 +/- 0.4 ml/kg/min) than in CC female patients (n = 17; 11.0 +/- 0.9 ml/kg/min). In summary, heterozigosity for the C34T allele of the AMPD gene is associated with reduced submaximal aerobic capacity in female patients with McArdle disease and might partly account, in this gender, for the variability that exists in the phenotypic manifestation of the disease.

Favorable Responses to Acute and Chronic Exercise in McArdle Patients

This study reports acute exercise responses in a large (N = 46) series of patients with McArdle disease and responses to exercise training in a smaller (n = 9) set of patients. Patients were studied during both incremental and steady-state cycle ergometer exercise, using cardiopulmonary testing, and the patients were compared with age- and gender-matched controls. The study was performed in a university setting (clinical exercise physiology laboratory). The 46 patients showed common features of McArdle disease. They were definitively diagnosed by histochemistry, biochemistry, and/or molecular genetic analysis. The 46 controls were healthy, sedentary individuals. Nine patients were studied before and after an 8-month supervised aerobic exercise training program (including five weekly sessions of walking and/or cycling exercise with a duration no greater than 60 minutes). The main indicators of exercise capacity that we measured were peak power output, peak oxygen uptake (VO2peak), and ventilatory threshold (VT). Exercise capacity (peak power output, 35% control; VO2peak, 44% control; VT, 66% control) was markedly depressed in the patients. The patients who trained improved peak power output (25%), VO2peak (44%), and VT (27%), with no evidence of negative outcomes from training. Although not achieving normal values, the response to training put the patients into the lower limit of normal controls. Under carefully controlled conditions, patients with McArdle disease may perform acute exercise safely, and they may respond favorably to training. This may offer an additional therapeutic option to help normalize the lifestyles of these patients.

Point:Counterpoint: Lactic acid accumulation is an advantage/disadvantage during muscle activity

Point:Counterpoint: Lactic acid accumulation is an advantage/disadvantage during muscle activity

Free Mg2+ concentration in the calf muscle of glycogen phosphorylase and phosphofructokinase deficiency patients assessed in different metabolic conditions by 31P MRS.

BackgroundThe increase in cytosolic free Mg2+ occurring during exercise and initial recovery in human skeletal muscle is matched by a decrease in cytosolic pH as shown by in vivo phosphorus magnetic resonance spectroscopy (31P MRS). To investigate in vivo to what extent the homeostasis of intracellular free Mg2+ is linked to pH in human skeletal muscle, we studied patients with metabolic myopathies due to different disorders of glycogen metabolism that share a lack of intracellular acidification during muscle exercise.MethodsWe assessed by 31P MRS the cytosolic pH and free magnesium concentration ([Mg2+]) in calf muscle during exercise and post-exercise recovery in two patients with McArdle's disease with muscle glycogen phosphorylase deficiency (McArdle), and two brothers both affected by Tarui's disease with muscle phosphofructokinase deficiency (PFK).ResultsAll patients displayed a lack of intracellular acidosis during muscle exercise. At rest only one PFK patient showed a [Mg2+] higher than the value found in control subjects. During exercise and recovery the McArdle patients did not show any significant change in free [Mg2+], while both PFK patients showed decreased free [Mg2+] and a remarkable accumulation of phosphomonoesters (PME). During initial recovery both McArdle patients showed a small increase in free [Mg2+] while in PFK patients the pattern of free [Mg2+] was related to the rate of PME recovery.Conclusioni) homeostasis of free [Mg2+] in human skeletal muscle is strongly linked to pH as shown by patients' [Mg2+] pattern during exercise;ii) the pattern of [Mg2+] during exercise and post-exercise recovery in both PFK patients suggests that [Mg2+] is influenced by the accumulation of the phosphorylated monosaccharide intermediates of glycogenolysis, as shown by the increased PME peak signal.iii) 31P MRS is a suitable tool for the in vivo assessment of free cytosolic [Mg2+] in human skeletal muscle in different metabolic conditions;

Molecular analysis of myophosphorylase deficiency in Dutch patients with McArdle's disease.

We report on 8 Dutch patients with McArdle's disease from 6 unrelated families. Molecular analysis revealed the presence of four previously described mutations: the common R49X mutation, the IVS14+1G>A mutation and the recently reported R269X and Y84X nonsense mutations; and two new molecular defects: a missense mutation R138W in the homozygous state in two siblings, and a frameshift mutation c.1797delT. This first genetic study of patients from The Netherlands with McArdle's disease confirms that the R49X mutation is also the most common in Dutch patients, and that there is genetic heterogeneity within this population. Moreover, our data support the hypothesis that the Y84X mutation is a relatively frequent mutation in McArdle's patients with a Central European background, and expand the already crowded map of mutations within the PYGM gene responsible for McArdle's disease.

Has the phoenix risen?

Has the phoenix risen?

Role of 5'AMP-activated protein kinase in glycogen synthase activity and glucose utilization: insights from patients with McArdle's disease.

It has been suggested that 5'AMP-activated protein kinase (AMPK) is involved in the regulation of glucose and glycogen metabolism in skeletal muscle. We used patients with chronic high muscle glycogen stores and deficient glycogenolysis (McArdle's disease) as a model to address this issue. Six McArdle patients were compared with control subjects during exercise. Muscle alpha2AMPK activity increased in McArdle patients (from 1.3 +/- 0.2 to 1.9 +/- 0.2 pmol min(-1) mg(-1), P = 0.05) but not in control subjects (from 1.0 +/- 0.1 to 1.3 +/- 0.3 pmol min(-1) mg(-1)). Exercise-induced phosphorylation of the in vivo AMPK substrate acetyl CoA carboxylase (ACCbeta; Ser(221)) was higher (P < 0.01) in McArdle patients than in control subjects (18 +/- 3 vs. 10 +/- 1 arbitrary units). Exercise-induced whole-body glucose utilization was also higher in McArdle patients than in control subjects (P < 0.05). No correlation between individual AMPK or ACCbeta values and glucose utilization was observed. Glycogen synthase (GS) activity was decreased in McArdle patients from 11 +/- 1.3 to 5 +/- 1.2 % (P < 0.05) and increased in control subjects from 19 +/- 1.6 to 23 +/- 2.3 % (P < 0.05) in response to exercise. This was not associated with activity changes of GS kinase 3 or protein phosphatase 1, but the changes in GS activity could be due to changes in activity of AMPK or protein kinase A (PKA) as a negative correlation between either ACCbeta phosphorylation (Ser(221)) or plasma adrenaline and GS activity was observed. These findings suggest that GS activity is increased by glycogen breakdown and decreased by AMPK and possibly PKA activation and that the resultant GS activity depends on the relative strengths of the various stimuli. Furthermore, AMPK may be involved in the regulation of glucose utilization during exercise in humans, although the lack of correlation between individual AMPK activity or ACCbeta phosphorylation (Ser(221)) values and individual glucose utilization during exercise implies that AMPK may not be an essential regulator.

Decreased insulin action in skeletal muscle from patients with McArdle's disease.

Insulin action is decreased by high muscle glycogen concentrations in skeletal muscle. Patients with McArdle's disease have chronic high muscle glycogen levels and might therefore be at risk of developing insulin resistance. In this study, six patients with McArdle's disease and six matched control subjects were subjected to an oral glucose tolerance test and a euglycemic-hyperinsulinemic clamp. The muscle glycogen concentration was 103 +/- 45% higher in McArdle patients than in controls. Four of six McArdle patients, but none of the controls, had impaired glucose tolerance. The insulin-stimulated glucose utilization and the insulin-stimulated increase in glycogen synthase activity during the clamp were significantly lower in the patients than in controls (51.3 +/- 6.0 vs. 72.6 +/- 13.1 micromol x min(-1) x kg lean body mass(-1), P < 0.05, and 53 +/- 15 vs. 79 +/- 9%, P < 0.05, n = 6, respectively). The difference in insulin-stimulated glycogen synthase activity between the pairs was significantly correlated (r = 0.96, P < 0.002) with the difference in muscle glycogen level. The insulin-stimulated increase in Akt phosphorylation was smaller in the McArdle patients than in controls (45 +/- 13 vs. 76 +/- 13%, P < 0.05, respectively), whereas basal and insulin-stimulated glycogen synthase kinase 3alpha and protein phosphatase-1 activities were similar in the two groups. Furthermore, the ability of insulin to decrease and increase fat and carbohydrate oxidation, respectively, was blunted in the patients. In conclusion, these data show that patients with McArdle's glycogen storage disease are insulin resistant in terms of glucose uptake, glycogen synthase activation, and alterations in fuel oxidation. The data further suggest that skeletal muscle glycogen levels play an important role in the regulation of insulin-stimulated glycogen synthase activity.

The exercise metaboreflex is maintained in the absence of muscle acidosis: insights from muscle microdialysis in humans with McArdle's disease.

1. In McArdle's disease, muscle glycogenolysis is blocked, which results in absent lactate and enhanced ammonia production in working muscle. Using McArdle patients as an experimental model, we studied whether lactate and ammonia could be mediators of the exercise pressor reflex. 2. Changes in muscle interstitial ammonia and lactate were compared with changes in blood pressure and muscle sympathetic nerve activity (MSNA) during static arm flexor exercise at 30% of maximal contraction force. Muscle interstitial changes in lactate and ammonia were assessed by microdialysis of the biceps muscle, and MSNA by peroneal nerve microneurography, in six McArdle patients and 11 healthy, matched controls. One McArdle patient also had myoadenylate deaminase deficiency, a condition associated with abolished ammonia production in exercise. 3. Exercise-induced increases were higher in McArdle patients vs. controls for MSNA (change of 164 +/- 71 vs. 59 +/- 19%) and blood pressure (change of 47 +/- 7 vs. 38 +/- 4 mmHg). Interstitial lactate increased in controls (peak change 1.3 +/- 0.2 mmol x l(-1)) and decreased in McArdle patients (peak change -0.5 +/- 0.1 mmol x l(-1)) during and after exercise. Interstitial ammonia did not change during exercise in either group, but was higher post-exercise in McArdle patients, except in the patient with myoadenylate deaminase deficiency who had a flat ammonia response. This patient had an increase in MSNA and blood pressure comparable to other patients. MSNA and blood pressure responses were maintained during post-exercise ischaemia in both groups, indicating that sympathetic activation was caused, at least partly, by a metaboreflex. 4. In conclusion, changes in muscle interstitial lactate and ammonia concentrations during and after exercise are temporally dissociated from changes in MSNA and blood pressure in both patients with McArdle's disease and healthy control subjects. This suggests that muscle acidification and changes in interstitial ammonia concentration are not mediators of sympathetic activation during exercise.

ASSESSING FUNCTIONAL CAPACITY IN MCARDLE??S PATIENTS WITH AN ADAPTED DUKE ACTIVITY STATUS INDEX AND A TWELVE MINUTE SHUTTLE WALK TEST

This study aimed to identify a practical and objective means of assessing functional capacity in McArdle's patients by the combined use of the ACSM recommended Duke Activity Status Index (DASI) questionnaire and a 12 minute shuttle walk test (12MSW). Participants were 18 McArdle's patients (9 male, 9 female) aged 45.6 (sd 9.4) yrs. Following ethical approval and informed consent, the participants completed the DASI and performed the 12MSW. The modified DASI questionnaire asked the participants to answer yes or no to being able to perform each of the 12 physical activities without getting severe muscle pain. The shuttle walk consisted of having participants complete as many 20 m shuttles as possible in 12 mins. As a means of preventing harmful muscle contracture, participants were instructed to regulate walking speed by not allowing leg pain to exceed level 4 on Borg's category ratio 0 – 10 rating of perceived pain scale (RPP). If RPP rose above level 4, participants were informed to either slow down or stop until they could resume a walking pace below this level. Heart rate, RPP and walking distance were recorded at the end of each minute of the 12MSW. The DASI scores ranged from 4.57 to 58.2, with a mean of 23.7. Distances walked in 12 mins ranged from 195 to 1180 m with a mean of 727.5 m. The accumulated distances walked at the end of each minute, between 3 and 12 min, were significantly correlated with DASI (Pearson's: range r = .59 to .61; p < .01). During the 12MSW, mean (sd) heart rates ranged between 59% (12) and 71% (18) of age predicted maximum. In conclusion, a simple timed shuttle walk that is regulated by RPP, lasting ≥ 3 min, provides support for the use of DASI to assess functional capacity in McArdle's patients.

ATP, phosphocreatine and lactate in exercising muscle in mitochondrial disease and McArdle's disease.

We studied exercise-induced changes in the adenosine triphosphate (ATP), phosphocreatine (PCr), and lactate levels in the skeletal muscle of mitochondrial patients and patients with McArdle's disease. Needle muscle biopsy specimens for biochemical measurement were obtained before and immediately after maximal short-term bicycle exercise test from 12 patients suffering from autosomal dominant and recessive forms of progressive external ophthalmoplegia and multiple deletions of mitochondrial DNA (adPEO, arPEO, respectively), five patients with mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) 3243 A-->G point mutation, and four patients with McArdle's disease. Muscle ATP and PCr levels at rest or after exercise did not differ significantly from those of the controls in any patient group. In patients with mitochondrial disease, muscle lactate tended to be lower at rest and increase more during exercise than in controls, the most remarkable rise being measured in patients with adPEO with generalized muscle symptoms and in patients with MELAS point mutation. In McArdle patients, the muscle lactate level decreased during exercise. No correlation was found between the muscle ATP and PCr levels and the respiratory chain enzyme activity.

Chapter 7 Interrelationships Between Metabolism Of Glycogen Phosphorylase And Pyridoxal Phosphate—Implications In Mcardle'S Disease

This chapter discusses the interrelationships between metabolism of glycogen phosphorylase and pyridoxal phosphate-implications in Mcardle's disease. Glycogen phosphorylase is the key regulator of glycogenolysis, catalyzing the phosphorolysis of glycogen to produce glucose-1-phosphate. The rate of degradation of phosphorylase measured by cofactor labeling is same as that measured by continuous infusion of radiolabeled amino acids. The principle of using radiolabeled vitamin B6 as a label for phosphorylase degradation is straightforward and takes the form of a classical pulse chase protocol. The chapter studies muscle-wasting processes in a mouse, and the role of degradation in muscle growth on the chicken. In McArdle's disease, the whole body phosphorylase-derived pool acts as a “buffer” to compensate for day-to-day variation in vitamin B6 intake. Analysis of the kinetics in McArdle's patients defines the role of muscle phosphorylase in the compartmentalization of vitamin B6.

McArdle's disease: Molecular genetics and metabolic consequences of the phenotype

McArdle's disease is defined as a lack of functional muscle glycogen phosphorylase. Analysis of the myophosphorylase gene has demonstrated substantial heterogeneity in the mutations that cause the disease, but in almost all individuals, the molecular phenotype is the absence of the protein in skeletal muscle. Muscle glycogen phosphorylase is a major repository of vitamin B6 in the body, accounting for at least 80% of the total body pool. In McArdle's patients, this pool is therefore missing, introducing the possibility that vitamin B6 metabolism might be altered in these individuals. Preliminary data have shown that McArdle's patients show signs of a subclinical vitamin B6 deficiency, and that oral vitamin B6 supplementation can improve vitamin B6 status and enhance fatigue resistance in muscle.

McArdle's disease: a nonsense mutation in exon 1 of the muscle glycogen phosphorylase gene explains some but not all cases.

McArdle's disease is an inherited disease that results from a lack of functional muscle glycogen phosphorylase. We report here the identification of a C to T transition in exon 1 of the muscle phosphorylase gene found in all patients studied. This base pair mutation results in the substitution of a stop codon (TGA) for the codon (CGA) for Arg49 in the mature protein, and generates a novel restriction site for NlaIII. Of sixteen McArdle's patients, ten are homozygous for this mutation; the remainder are heterozygous. Additional unidentified mutations must lead to the McArdle's phenotype in the latter group of patients.

Increased muscular β‐hydroxyacyl CoA dehydrogenase with McArdle's disease

Enzymes of energy production were measured in muscle homogenates and in individual muscle fibers from 5 patients with McArdle's disease. Individual fibers were investigated to determine whether fibers of all types were completely devoid of glycogen phosphorylase activity and whether the involved fibers might be biochemically altered in a fiber type dependent manner to enhance the energy-generating capabilities of the cells through other metabolic pathways. Using highly sensitive biochemical assays, a complete absence of glycogen phosphorylase, a and b, activity was found in fibers of all types in the McArdle's patients. Levels of enzymes representing glycolysis, the Krebs cycle, and high energy phosphate metabolism were essentially normal in each fiber type, indicating an apparent lack in metabolic adaptation of these energy pathways to the absence of glycogen utilization. However, a key enzyme in the beta-oxidation of fatty acids (beta-hydroxyacyl CoA dehydrogenase, beta OAC) was elevated in all patients, and substantially in 4 of the 5. This suggested that lipid substrates can provide support for oxidative endurance capacity in some patients. Individual fiber analyses indicated that the compensation involved fibers of all types.

Exercise and recovery ventilatory and VO2 responses of patients with McArdle's disease

This study was designed to determine whether patients with McArdle's disease, who do not increase their blood lactate levels during and after maximal exercise, have a slow "lactacid" component to their recovery O2 consumption (VO2) response after high-intensity exercise. VO2 was measured breath by breath during 6 min of rest before exercise, a progressive maximal cycle ergometer test, and 15 min of recovery in five McArdle's patients, six age-matched control subjects, and six maximal O2 consumption- (VO2 max) matched control subjects. The McArdle's patients' ventilatory threshold occurred at the same relative exercise intensity [71 +/- 7% (SD) VO2max] as in the control groups (60 +/- 13 and 70 +/- 10% VO2max) despite no increase and a 20% decrease in the McArdle's patients' arterialized blood lactate and H+ levels, respectively. The recovery VO2 responses of all three groups were better fit by a two-, than a one-, component exponential model, and the parameters of the slow component of the recovery VO2 response were the same in the three groups. The presence of the same slow component of the recovery VO2 response in the McArdle's patients and the control subjects, despite the lack of an increase in blood lactate or H+ levels during maximal exercise and recovery in the patients, provides evidence that this portion of the recovery VO2 response is not the result of a lactacid mechanism. In addition, it appears that the hyperventilation that accompanies high-intensity exercise may be the result of some mechanism other than acidosis or lung CO2 flux.

Molecular mechanisms of McArdle's disease (muscle glycogen phosphorylase deficiency). RNA and DNA analysis.

Lack of muscle glycogen phosphorylase activity leads to McArdle's disease, a rare metabolic myopathy. To investigate its molecular basis at the nucleic acid level, we isolated muscle phosphorylase cDNA clones from a human cDNA library in Escherichia coli plasmid pBR 322. Subcloning of one insertion of M13 bacteriophage permitted its definite identification by sequencing. Northern blot experiments revealed one specific messenger RNA of 3.4 kilobases found uniquely in tissues expressing muscle phosphorylase. We show that McArdle's disease exhibits a molecular heterogeneity at the messenger RNA level. In eight unrelated cases of McArdle's disease in which no inactive proteins had been detected, we assayed muscle biopsies for phosphorylase mRNA by Northern blotting. In five cases, no muscle phosphorylase mRNA could be detected, while in three other cases, normal length mRNA was present in lower amounts. Moreover, Southern blot analysis of DNA isolated from white blood cells in four McArdle patients revealed no major deletion or rearrangements of the phosphorylase gene as compared with controls.

The pathophysiology of McArdle's disease: clues to regulation in exercise and fatigue.

Muscle phosphorylase deficiency (McArdle's disease) has conventionally been considered a disorder of glycogenolysis, and the associated impairment in oxidative metabolism has been largely overlooked. Muscle glycogen normally is the primary oxidative fuel at exercise work loads requiring more than 75-80% of maximal O2 uptake (VO2max). Evidence is presented to support the hypothesis that a limited flux through the Embden-Myerhof pathway in McArdle's disease reduces the capacity to generate NADH required to support a normal VO2max. The extent of the oxidative defect is substrate dependent; i.e., it can be partially corrected by increasing the availability of alternative oxidative substrates (e.g., glucose, free fatty acids) to working muscle. Experiments employing modification of substrate availability closely link the hyperkinetic circulatory response to exercise (i.e., an abnormally large increase in O2 transport to skeletal muscle) and the premature muscle fatigue and cramping of McArdle patients with their oxidative impairment and suggest that a metabolic common denominator in these abnormal responses may be a pronounced decline in the muscle phosphorylation potential ([ATP]/[ADP][Pi]). The hyperkinetic circulation likely is mediated by the local effects on metabolically sensitive skeletal muscle afferents and vascular smooth muscle of K+, Pi, or adenosine or a combination of these substances released excessively from working skeletal muscle. The premature muscle fatigue and cramping of McArdle patients does not appear to be due to depletion of ATP but is associated with an increased accumulation of Pi and probably ADP in skeletal muscle. Accumulations of Pi and ADP are known to inhibit the myofibrillar, Ca2+, and Na+-K+-ATPase reactions.